Process for synthesis for mercaptans



United States Patent PR6ES FOR SYNTEESIS FOR MERCAPTANS Paul F. Warnerand Richard D. Franz, Phillips, Tex.,

assignors to Phillips Petroleum Company, a corporation of Delaware NoDrawing. Filed Oct. 20, 1961, Ser. No. 146,458 7 Ciaims. (Cl. 260-609)This invention relates to an improved process for preparing mercaptansby reacting an olefin with H S utilizing a novel catalyst, and to thenovel catalyst for the process.

The synthesis of mercaptans by reacting H S with an olefin is aconventional process. When utilizing relatively high molecular weightolefins, such as those containing from 9 to 16 carbon atoms permolecule, conducting the reaction at usual reaction temperatures withthe conventional catalyst, H PO -BF the yield of high molecular weightmercaptans is substantially reduced by fracturing of the olefins andproduction of a substantial proportion of lower molecular weightmercaptans. To illustrate, when reacting triisobutylene with H S toproduce tertiary dodecylmercaptan, a substantial amount of butyl andoctyl mercaptans are produced. However, reduction of the temperature ofthe reaction below that at which fracturing of the heavy olefin isavoided results in low yield due to low activity of the catalyst H PO-BF at low temperatures. This invention is concerned with a more activecatalyst for mercaptan synthesis at low temperatures.

Accordingly, it is an object of the invention to provide a process forpreparing mercaptans utilizing an improved catalyst. Another object isto produce mercaptans in improved yields at low temperatures. A furtherobject is to provide an improved catalyst for the synthesis ofmercaptans and by reacting H S and an olefin. It is also an object ofthe invention to provide an improved process for the synthesis ofmercaptans containing from 9 to 16 carbon atoms per molecule withimproved yield at low temperature. An additional object is to provide animproved catalyst containing the complex H PO -BF or H PO 'BF which ismore effective at low temperatures than this complex alone. Otherobjects of the invention will become apparent to one skilled in the artupon consideration of the accompanying disclosure.

A broad aspect of the invention comprises a catalyst consistingessentially of a liquid complex of an oxygencontaining acid ofphosphorus, an alcohol of 1 to carbon atoms, and BF This catalyst isprepared by mixing the acid and the alcohol and adding BF to themixture, preferably to saturate the mixture with B1 for highest activityof the catalyst. The preferred acid is H PO but H PO is also effective.(It is to be understood that Where the ensuing disclosure refers to H POor phosphoric acid, H PO or phosphorus acid may be used.) Theconcentration of phosphoric acid is not critical and the commerciallyavailable grade of 85% concentration is generally used. However,concentrations in the range of 40 to 100% are effective.

' The alcohols useful in the catalyst are the C to C alcohols includingethyl, methyl, propyl, butyl, and the amyl alcohols. The ratio ofalcohol to the acid in the mixture is in the range of 1:9 to 1:1 byweight vto be most effective. However, proportions outside of this rangehave some advantage in the catalyst. The BF should be added to theliquid mixture of acid and alcohol to the saturation point to providethe most active catalyst, but lesser amounts produce a catalyst ofproportionately less activity.

Another aspect of the invention comprises reacting H 8 with an olefinichydrocarbon in admixture with the H PO -BF alcohol complex to producethe corresponding mercaptan. This process produces high yield of mer-3,137,735 Patented June 16, 1964 captan, particularly, at temperaturesin the range of -90 to 0 F. and preferably in the range of to -20 F. Theprocess is conducted at pressures sufiicient to maintain the reactantsin liquid phase at reaction temperatures. Pressure depends upon thereactant mixture but pressures in the range of about 50 to 500 p.s.i.g.are generally suitable. Conventional mol ratios of H 8 to olefin such as1:1 to 6:1 and preferably 2:1 to 5:1 may be used. The volume ratio ofhydrocarbon feed to catalyst is in the ice range of about 5:1 to 15:1.

The olefinic hydrocarbons which may be reacted with hydrogen sulfide incarrying out this invention are those containing at least one ethylenicbond; and include aliphatic olefins, cyclic olefins, and substitutedaliphatic and cyclic olefins in which the substituting group or groupsmay be hydrocarbon or non-hydrocarbon radicals of such character thatthey do not interfere with the primary reaction. Typical olefins includeethylene, butylenes, cyclohexene, triisobutylene, and other C to Colefins.

Tertiary dodecyl mercaptan made from triisobutylene is particularlyuseful as a rubber modifier. Numerous synthesis runs have been madereacting triisobutylene with H 5 in admixture with H PO -BF catalyst andwith H PO -BF 'CH OH. The following examples. illustrate the use of theconventional catalyst H PO -BF and the catalyst of the invention inthese runs.

EXAMPLE I Triisobutylene was reacted with hydrogen sulfide in admixturewith boron trifiuoride-phosphoric acid catalyst made by saturating 85%phosphoric acid with boron trifluoride. The BF content of the catalystwas about 55 weight percent. The feed stock was prepared by blending thetriisobutylene with hydrogen sulfide in a steel cylinder fitted with aneductor tube. The feed was metered with a Lapp pump through a pressurecontrolled relief valve into the reactor containing the catalyst. Theefiiuent passed through the phase separator and through another pressurecontrolled relief valve where the excess hydrogen sulfide flashed out.The crude mercaptan was collected in 1000 ml. cuts.

Synthesis conditions observed throughout the various four passoperations were as follows: hydrogen sulfide to olefin mole ratio ofabout 1.5; hydrocarbon to catalyst volume ratio in the reactor, about 9;feed rate of 1000-ml. of liquid efiluent per hour; and pressure 350p.s.i.g. This pressure was chosen as being high enough to keep thereactants in liquid phase at all of the temperatures tested.

, The liquid hydrocarbon efiluent was cut into three fractions, C and Cmercaptans (IBP to 340 F.), recycle TIB (340 to 400 F.), and crude Cmercaptan (kettle product) in a Vigreaux column. The crude C mercaptanwas further purified by distillation in a %-inch O.D. by 4-foot long,spinning band column. The unreacted olefin from the first pass wasrecycled with fresh H 8 to the second pass. The unreacted olefin fromthe second pass Wasrecycled with H 5 to the third pass, etc., for fourpasses.

Data obtained in the runs are presented in Table I.

Table 1 Dodeeyl Mercaptan Olefin Yield, mole percent ReactionTemperature, F. Conversion Per Pass Per Pass Ultimate Table 11 Weightpercent Catalyst Component Bra-Harm nrg-rnroi-cmon The yield per passobtained with the B1 H PO Gil- H was 20 mol percent and the ultimateyield of tertiary dodecyl mercaptan was 87 mol-percent. This rundemonstrates the more effective character of the catalyst of theinvention at low temperatures, such as -40 F., as compared with BF -H POcatalyst.

The BF in the catalyst forms a complex with both the H PO and thealcohol and the alcohol renders the catalyst complex less viscous thanthe H PO -BF complex.

Certain modifications of the invention will become apparent to thoseskilled in the art and the illustrative details disclosed are not to beconstrued as imposing unnecessary limitations on the invention.

We claim:

1. A process for preparing a mercaptan which comprises contacting a C toC olefin hydrocarbon with hydrogen sulfide in admixture with a catalystsystem consisting essentially of BF -H PO -ROH wherein R is alkyl of 12,137,584" Ott Nov. 22, 1938 2,390,099 Harmon Dec. 4, v1945 2,426,647Schulze et al. Sept.2, 1947 v 2,470,175 Linn May 17, 1949 2,491,116Kraus et al Dec-13, 1949 2,498,872 Bell et al Feb. 28, 1959 2,502,596Schultz "Apr. 4, 1950 2,865,965 May et a1 Dec. 23, 1958 7 2,943,063 Ebyet al. June 28, 1960 FOREIGN PATENTS 501,697

to 5 carbon atoms under reaction conditions including a temperature inthe range of 90 to 0 F. and sufficient pressure to maintain thereactants in liquid phase such that mercaptan is formed.

2. The process of claim 1 wherein said olefin comprises triisooutyleneand dodecyl mercaptan is formed.

3. The process of claim 1 wherein R is CH .4. The process of claim 1wherein the ratio of alco' hol to phosphoric acid is in the range of 1:9to 1:1 by Weight and the phosphoric acid-alcohol mixture is saturatedWith BP 5. The process of claim 1 wherein the temperature of contactingis in the range of to 20.

6. A process for preparing tertiary dodecyl mercaptan which comprisesreacting triisobutylene with hydrogen sulfide in admixture with acatalyst system comprising a mixture of an oxygen-containing acid ofphosphorus and a C to C alcohol in a Weight ratio of alcohol to acid inthe range of 1:9 to 1:1 saturated with B1 at a reaction temperature inthe range of to 0 P. so as to form said mercaptan; and recovering saidmercaptan.

'7. The process of claim 6 wherein said acid is H PO said alcohol ismethanol, and the methanol-B 1 0 ratio is a weight ratio in the range of1:4 to 2:3.

References Cited in the file of this patent UNITED STATES PATENTS CanadaApr. 20, 1957

1. A PROCESS FOR PREPARING A MERCAPTAN WHICH COMPRISES CONTACTING A C9TO C16 OLEFIN HYDROCARBON WITH HYDROGEN SULFIDE IN ADMIXTURE WITH ACATALYST SYSTEM CONSISTING ESSENTIALLY OF BF3$H3PO4$ROH WHEREIN R ISALKYL OF 1 TO 5 CARBON ATOMS UNDER REACTION CONDITIONS INCLUDING ATEMPERATURE IN THE RANGE OF -90* TO 0*F. AND SUFFICIENT PRESSURE TOMAINTAIN THE REACTANTS IN LIQUID PHASE SUCH THAT MERCAPTAN IS FORMED.